feat(components): add Tile

Supports #34

TODO:

- remove exported props
- compose TileGroup, SelectableTile, RadioTile components

src/components/Tile/TileGroup.svelte

@@ -0,0 +1,19 @@
+<script>
+  let className = undefined;
+  export { className as class };
+  export let disabled = false;
+  export let legend = '';
+
+  import { cx } from '../../lib';
+
+  $: _class = cx('--tile-group', className);
+</script>
+
+<fieldset class={_class} {disabled}>
+  {#if legend}
+    <legend>{legend}</legend>
+  {/if}
+  <div>
+    <slot />
+  </div>
+</fieldset>